Heterocyclic catalysts for esterification of aromatic dicarboxylic acids with cyclic carbonates of alkylene gylcols



United States Patent Oflice 3,549,692 Patented Dec. 22, 1970 rm. (:1. cos 17/015 US. Cl. 260-475 4 Claims ABSTRACT OF THE DISCLOSURE Esterification of aromatic dicarboxylic acids with cyclic carbonates of alkylene glycols in the presence of fivemembered aromatic N-heterocyclic compounds containing two to four heterocyclic nitrogen atoms and transesterification of resulting esters to produce high molecular weight, fiber-forming polyesters.

The present invention relates to improvements in the production of esterification products of aromatic dicarboxylic acids by reacting said aromatic dicarboxylic acids under esterification conditions with cyclic carbonates of alkylene glycols in the presence of catalysts, and more especially to the use of heterocyclic nitrogen compounds as catalysts for the aforementioned reaction.

It is known to react terephthalic acid with cyclic 1.2- glycol-carbonates at elevated temperatures to give oligoand poly-terephthalic acid glycol esters (US. patent specification Nos. 2,802,807 and 2,799,677).

The catalysts hitherto used for accelerating this reaction, such as alkali metal carbonates, antimony trioxide, cerium dioxide, zinc borate, magnesium acetate, lead acetate, and the like, prove to be little efiective at the desired low reaction temperatures (about 160-220" C.). They necessitate long reaction times which promote side reactions, such as ether formation, and cause discolorations in the reaction product.

According to the present invention tautomeric, fivemembered aromatic N-heterocycles containing two to four heterocyclic nitrogen atoms are used as catalysts for the reaction of aromatic dicarboxylic acids with cyclic glycol carbonates.

It has been found that, surprisingly, the catalytic effectiveness of these compounds by far surpasses that of the known catalysts and that the aforementioned disadvantages are obviated in their use.

Examples of the catalysts to be used according to the invention are the following: imidazole, Z-aIkyI-imidazoles, preferably such having l4 carbon atoms in the alkyl group, for instance 2-methyl-, 2-allyl-benzimidazole, dialkyl imidazoles having 14 carbon atoms in the alkyl group such as 2,4- or 4,5-dimethyl imidazoles, benzimidazole, 2-alkyl-benzimidazole, such as Z-methylor 2-alkly-benzimidazoles having 14 carbon atoms in the alkyl group, pyrazole, benzopyrazole, triazole, 3,5-dimethyl-1, 2,4-triazole, tetrazole, S-phenyl-tetrazole. The catalysts are expediently used in amounts of about 0.01 to about 5% by weight, as calculated on the weight of the reactants. The preferred catalysts are imidazole and derivatives of imidazoles.

The catalysts may be used in each case by themselves, but also in admixture with one another, as well as in admixture with oxides of the metals of Groups IV, V and VI (including both Chief and Minor Sub-Groups) of the Mendeleev Periodic Classification, such as titanium, germanium, tin, antimony, lead, bismuth, niobium, tantalum, thorium, uranium.

Suitable aromatic dicarboxylic acids with which the cyclic glycol carbonates can be reacted are, for example terephthalic acid, phthalic acid, isophthalic acid, naphalenedicarboxylic acids, such as 1,'8, -1,4, -1,2, hydroxyphenyl-dicarboxylic acid such as Z-hydroxy-terephthalic acid, S-hydroxy-isophthalic acid, 4-hydroxy-phthalic acid, and alkyl-phenyl-dicarbox.ylic acids, such as 2- rnethyl-terephthalic acid, B-methyII-phthalic acid, tetramethyl-phthalic acid. S-isobutyl-isophthalic acid. The preferred acid is terephthalic acid.

Cyclic carbonates which are suitable for the reaction with the aromatic dicarboxylic acids are the cyclic carbonates of ethylene-glycol and l,2-propane-dio1.

The aromatic dicarboxylic acid is expediently reacted with the cyclic glycol carbonate in ,a molar ratio of about 1:2, at temperatures between and 250 C., preferably at to 220 (3., in the presence of the above catalysts, to give essentially aromatic dicarboxylic acid-bis-fi-hydroxyalkyl esters which may be transesterified in a second process step known as such to give fibre forming polyesters. It is also possible to start. the reaction with a molar ratio of aromatic dicarboxylic acid to cyclic glycol carbonate of 1:0.5 to 1: 1.5 and to add the remaining portion of glycol carbonate to the reaction mixture in the degree as dicarboxylic acid-bis-fi-hydroxyalkyl ester is formed.

The molar proportions of total dicarboxylic acid and total cyclic carbonate may vary Ibetween about 1:1.5 and 1:2, and mixtures of dicarboxylic acid monoand -bishydroxyal kyl esters, oligoand non-fibre forming polydicarboxylic acid glycol esters are formed when using the reactants in a proportion other than 1:2. These mixtures are also capable of being transesterified in a second process step to give fibre forming polyesters.

This transesterification to produce high molecular weight, fibre forming polyesters may be carried out at temperatures of about 250 to 300 0, preferably under low presusre, for example a pressure of the order of 5 mms. of mercury or less. This reaction may be carried out in the presence of an ester-interchange catalyst known as such. Suitable ester-interchange catalysts are the above cited oxides of the metals of Groups IV, V and VI of the Mendeleev Periodic Classification. As indicated above it is preferred to apply these catalysts together with the heterocyclic catalysts of the invention, however, it is also possible to introduce the ester-interchange catalysts into the reaction mixture at the beginning of the second process step. The ester-interchange catalysts may be used in amounts of 0.1 to 2% by weight as calculated on the weight of the reaction mixture.

The following examples illustrate the process according to the invention.

' EXAMPLE 1 41.5 parts by weight terephthalic acid mol), 44.0 parts by weight cyclic ethylene glycol carbonate /2 mol) and 0.085 part by weight of one of the catalysts, described below in more detail, are intimately mixed. In a flask, the mixture is placed into a heating bath which is constantly kept at 200 C., while stirring. The temperature in the reaction flask amounts to about C. The time required for splitting of 5.6 liters CO is taken as the measurement for the effectiveness of the catalyst.

After splitting oh the total amount of CO the ester obtained with imidazole as catalyst has an acid number of 3 to 4 and an OH number of 2390.

Table I shows the results of the experiments:

TABLE I Time for Splitting Bath off 5.6

temperature litres CO Catalyst as C. mins Number:

(a) Imidazole 200 29 (b) Imidazole plus 0.085 part by 200 53 weight antimony trioxlde.

(e) Benz'nnidazole 200 36 (d) 2-methylbenzimidazole 200 48 (e). Potassium carbonate" 200 73 (f) Triphenylphosphinm 200 75 (g) Sodium carbonate 200 93 (11)..... Calcium acetate 200 109 (i) Barium acetate 200 112 (j) Antimony trloxldc. 200 113 (k) Magnesium acetate 200 126 (l) Dibutyl tin ox1dc 200 129 (m) 1 Tricycloh exylphosphine 200 132 (n) Lead(II)-aeetat 200 152 (o). Cerium dioxid. 200 157 (p) 200 182 ((1)0..- 200 230 EXAMPLE 2 41.5 parts by weight terephthalic acid 41 mol), 44.0 parts by weight cyclic ethylene glycol carbonate /2 mol) and 0.085 part by weight of one of the catalysts, described below in more detail, are treated as in Example 1. The temperature of the heating bath amounts to 230 C. (about 195 C. in the reaction flask). After splitting off the total amount of CO the ester obtained with imidazole as catalyst has an acid number of 3 to 4 and an OH number of 388 to 390.

Table II shows the results of the experiments.

TABLE II Tiine for sp itting Bath oti 5.6 temperature litres CO Catalyst as C. mins Number (a) Imidazolz 230 15 (b). Imidazole plus 0.085 part by 230 16 weight antimony trioxide. (e) Benzimidazole 230 19 (d) Z-methylbenzimidazole 230 23 (e) Benzotriazole 230 27 (f). Dimethyl-1,2,4-triazole 230 27 (g). 3,5-dimethylpyrazole 230 28 (h) 5-pheny1tetrazo1e 230 37 (i) Zine borate 230 52 (k) Magnesium acetate 230 53 (l) Aluminium triehloride 230 60 (m) Nil 230 62 EXAMPLE 3 41.5 parts by weight phthalic acid A1, mol), 44.0 parts by weight cyclic ethylene glycol carbonate /2 mol) and 0.085 part by weight of one of the catalysts, described below in more detail, are treated as in Example 1. The temperature of the heating bath amounts to 230 C.

(a) Catalyst: imidazole;

5.6 litres CO were split off with 60 minutes. (b) Catalyst: potassium benzoate;

5.6 litres CO were split off within 162 minutes. (c) Catalyst: magnesium acetate;

only 0.6 litre CO were split otf within 220 minutes. (d) Catalyst: antimony trioxide;

only 1.5 litres CO were split off within 220 minutes. (e) Catalyst: nil;

only 1.5 litres CO were split off within 220 minutes.

EXAMPLE 4 41.5 parts by Weight terephthalic acid mol), 51.0 parts by weight propylene glycol-1,2-carbonate and 0.092 part by weight of one of the catalysts, described below in more detail, are treated as in Example 1. The temperature of the heating bath amounts to 230 C.

(a) Catalyst: imidazole;

5.6 litres CO split off within 51 minutes. (b) Catalyst: potassium benzoate;

3.05 litres CO split off within 200 minutes. Catalyst: magnesium acetate;

2.65 litres CO split off within 200 minutes. (d) Catalyst: antimony trioxide;

only 0.5 litre CO are split off within 200 minutes. (e) Catalyst: nil;

0.7 litre CO split 011 within 200 minutes.

EXAMPLE 0.2 mole (50.8 g.) of terephthalic acid diglycol ester obtained according to the prescription of Example 2 is mixed with 0.04 mole-percent of calcium acetate and 0.01 mole-percent of antimony-III-oxide. The mixture is subjected while stirring and under nitrogen to the following conditions of time/ temperature/pressure:

Time, Tempera- Pressure,

minutes ture, C. torr During the heating 0.18 mole (11.2 g.) of glycol are distilled 01f. Thereafter the melt is kept while stirring for minutes at a temperature of 185 C. and under a pressure smaller than 0.5 torr. The product obtained has a relative viscosity of 1.87 measured at 25 C. in a solution containing 10 g. of the product dissolved in 1,000 ml. of a solvent consisting of 1 part by weight of phenol and 1 part by weight of tetrachloro ethane.

What we claim is:

1. A process for producing an ester of an aromatic dicarboxylic acid and a cyclic glycol carbonate, said process comprising reacting an aromatic dicarboxylic acid and a cyclic glycol carbonate at a temperature between 120 and 250 C. and in the presence of a catalytic amount of a five-membered aromatic N-heterocyclic compound containing two to four heterocyclic nitrogen atoms.

2. The process of claim 1 wherein said catalyst is an imidazole.

3. The process of claim 1 wherein catalytic amounts of oxides of the metals of Groups IV, V and VI of the Mendeleev Periodic Classification are used together with said aromatic N-heterocyclic compound.

4. The process of claim 1 wherein said aromatic dicarboxylic acid is terephthalic acid and said cyclic glycol carbonate is cyclic ethylene glycol carbonate.

References Cited UNITED STATES PATENTS 3,462,395 8/1969 Wiener 260- 3,050,548 8/1962 Munro 260-475 3,055,868 9/1962 McIntyre 260-75 3,215,731 11/1965 Bearden 260-486 2,789,964 4/1957 Reynolds et al. 260-47 2,799,664 7/1957 Drewitt et a1 260-45.4 2,870,124 1/1959 Ham 260-75 3,211,702 10/1965 Van Gijzen 260-77.5 3,329,652 7/1967 Christie 260-47 OTHER REFERENCES Bruice, Fife, Bruno, Benkovic, J. Am. Chem. Soc., 84, 3012-13 (1962).

JOSEPH L. SCHOFER, Primary Examiner C. A. HENDERSON, JR., Assistant Examiner U.S. Cl. X.R. 

